It has been conventionally known a HUD device equipped to a moving body and projecting an image on a projection surface of the moving body so that the image can be visually recognized as a virtual image from an inside of the moving body. In a first optical path disclosed in patent literature 1, a backlight, a projecting lens and an image displaying panel are arranged as an indicator. The backlight includes a light source emitting a light, a condensing lens and a diffusing board. The image displaying panel is a liquid crystal panel. The image displaying panel luminously displays an image by using a light of the light source having passed through a first optical path and projects the image on a projection surface via a second optical path.
However, since a mirror is not arranged in the first optical path of a HUD device disclosed in the patent literature 1, the first optical path has to be formed in a straight line. Therefore, when the HUD device is equipped to the moving body such as a vehicle, it is difficult to secure a sufficient geometrical distance in a limited space. In such a first optical path, a projecting lens with a short focal distance has to be arranged close to the light source. As a result, the light of the light source enters the liquid crystal panel with an uneven illuminance before the light spreads to an entire of a screen of the liquid crystal panel, and thereby to cause an uneven luminance in the image displayed on the liquid crystal panel.
On the other hand, when plural mirrors are arranged in the first optical path, a size of the HUD device is enlarged as the number of the mirrors increases, and it is difficult to equip the HUD device to the moving body such as a vehicle.